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Mistaking a murderer – Eyewitness memory blindness

Think about many of the decisions you make. Often, people can articulate reasons why they made a particular choice. Why are you voting for that presidential candidate? Why did you order chicken instead of fish? Why do you like soccer better than football? Not only could you describe why you made each of these decisions, but the options for each are clearly differentiated in memory, and thus easy to remember. If you voted for Bernie Sanders, and I asked you why you voted for Ted Cruz, you would correct my mistake easily.

At other times, choices are made on weaker memories. For example, if you're deciding what kind of peanut butter you need to buy, you might try to conjure up an image of what is in your pantry. Buying chunky instead of smooth peanut butter might not be a deadly mistake, but the American legal system relies on such memory evaluations in eyewitness testimony all the time. In testifying about witnessing a crime, people have to make decisions like who they saw robbing a store, based on memories that were formed under high stress and low information.

In these cases your memory for which choice you made will be much weaker and more susceptible to manipulation. A recent set of studies has described the illusion that they call choice blindness. For an example, see this demonstration:

In one of the first choice blindness studies, experimenters in a local supermarket gave customers a set of flavors of jam, and the participant is asked to pick which one is his favorite (obviously strawberry). Then, the participant is given a second taste of the non-preferred jam (probably grape), which he believes came from the strawberry jar, and is asked why he chose grape. Astoundingly, only between 33% and 50% of people indicated at all that they had been given the non-preferred flavor, even though most people indicated that they could taste the difference. Critically, this paradigm employed misinformation. The participant presumes that the jar contains the same flavor both times, when in fact, the experimenter turns the jar over, and scoops the opposite flavor from a hidden compartment in the bottom.

If people are blind to choices they make, this has clear and important consequences for the legal system, which relies on eyewitness testimony and memory. A group of researchers led by Kevin Cochran and Elizabeth Loftus, who has profoundly influenced the criminal justice system by exposing the weaknesses of human memory used as evidence, recently published a paper in the Psychonomic Society’s journal Memory and Cognition investigating whether people are susceptible to choice blindness when identifying criminals.

Cochran and colleagues had participants watch a slide show in which one character has her wallet stolen by one of the other three characters. Participants then answered questions that might be heard in a police interview, like "what color was the thief's jacket?" Answer choices were provided on a scale with 15 options (in the case of jacket colors, 15 color swatches were provided). Next, the experimenter showed participants a report in which some items had been manipulated (Misinformation items) by being moved four places away on the scale. That is, if a participant chose a light blue color swatch, they would see a report with the option four colors away selected. After a delay, participants were then given a memory test, in which they had to respond to the original questionnaire again. Consistent with prior choice blindness findings, the researchers found a significant bias in the results of the memory test toward the falsified responses.

In a second study, participants were shown a different slide show of a man stealing a radio from a car, and were asked to identify the man from a lineup of six men. After choosing, the participant was shown either a) a non-chosen person from the same lineup (Confirming condition), b) the person they chose (Manipulated condition), or c) no one (Control condition), and asked to write down why they chose that person. After a delay, participants were shown the same lineup again in a randomized order, asked to choose a person, and also asked to rate their confidence in their choice. This time, almost half of the participants in the Manipulated condition detected the change. For those who detected the manipulation, only 13% changed the person they identified as stealing the radio. For those who did not detect the manipulation, over half of them changed the person they identified. Most of these participants instead chose the person they had erroneously been shown (the misinformation).

Human memory is very labile. Understanding and demonstrating that this is true is critical for extracting unbiased witness testimony, and evaluating its trustworthiness.

In Netflix's recent smash hit Making a Murderer (Spoilers follow), choice blindness and misinformation may have played a powerful role. In questioning the young Brendan Dassey, police officers repeatedly feed him information.

For example, the officers tell Dassey that they found parts of a body near a fire pit and that they "know [he] saw some flesh." (page 451, pdf) Whether Dassey did see flesh or not, one possibility is that the officers' misinformation infiltrated Brendan's memory. So when Brendan says he was at the fire pit, and officers, in their question, change his testimony to suggest that he saw a body at the fire pit, Brendan's memory (and his realization that this is a fabrication, not his own actual memory) become The fallibility identified and described in Cochran and colleagues' study is twofold. First, human memory itself is susceptible to bias and compromise. Second, and what the choice blindness paradigm exposes, our ability to discriminate what is a real memory from what is a fabricated one is itself subject to falsification. Learning these lessons has enormous implications for a legal system that relies not just on the memory of witnesses, but on the memory of jurors whose job it is to evaluate evidence and testimony.